Definition
An altimeter that, in addition to displaying altitude to the pilot, electronically sends the aircraft's pressure altitude to the transponder so it can be transmitted to air traffic control as Mode C altitude information.
Plain English
An altimeter that does two jobs: it shows the pilot the altitude on the dial, and it also sends the altitude data to the transponder so controllers can see it on their radar screen.
Context Anchor
Seen in instrument flying, transponder, and Mode C altitude-reporting discussions.
Derivation
‘Encoding’ comes from ‘code’ — turning information into a signal that can be transmitted. The altimeter encodes the altitude reading into a digital signal the transponder can send out.
Why Pilots Care
ATC relies on accurate encoded altitude for vertical separation, traffic advisories, and terrain clearance.
Analogy
It is like a thermometer that not only shows the temperature on its face, but also sends the temperature to another device in a digital message.
Intuition Check
Do not assume the encoding altimeter simply broadcasts the exact altitude you see after setting the local pressure. For altitude reporting, it sends pressure altitude based on the standard 29.92 setting.
Example Sentence 1
Before takeoff, the pilot confirmed the encoding altimeter was working by asking ground control to verify the Mode C readout.
Example Sentence 2
Before takeoff the pilot verifies that the encoding altimeter is functioning so ATC will receive accurate altitude information.